1. Field of the Invention
The present invention relates generally to a method and apparatus for transporting individual semiconductor wafers in semiconductor processing applications, and more particularly to a method and apparatus for transferring wafers from wafer cassettes to a wafer processing chamber, such as a chemical vapor deposition reactor.
2. Description of the Background Art
Semiconductor processing operations in general require a very high throughput of wafers in order to reduce the processing cost of each individual integrated circuit. Such rapid processing, however, requires that the wafers be precisely and carefully handled and that very clean conditions be maintained at all times. Imprecise handling of wafers, which allows undesired contact between the wafers and the reactor and other surfaces, can both damage the circuits formed thereon and result in the generation of particulates which can diminish cleanliness and interfere with subsequent processing steps. Thus, it is a common goal of semiconductor process designers to be able to increase wafer throughput without resorting to imprecise wafer handling techniques which can damage the wafers and result in generation of particulate contaminants.
The ability to manipulate individual wafers during semiconductor processing is further complicated in high temperature systems, such as chemical vapor deposition reactors, where thermal cycling over wide temperature ranges can result in deformation of the wafer support platforms and loss of mechanical repeatability in the system, such as the susceptors in epitaxial deposition processes. Such deformation makes it very difficult to design mechanical systems for wafer transfer, since the precise locations of the wafer supports within the reactor will vary over time. Moreover, the need for wafers to cool prior to being returned to wafer cassettes further slows down the processing time for high temperature processes.
Therefore, it would be desirable to provide a method and system for rapidly transferring semiconductor wafers to and from a processing chamber in a manner which minimizes impact and contact between the wafers and the transporting equipment. It would be particularly desirable if such methods and systems provided for intermediate cooling of the wafers after they are removed from the processing chamber and before they are replaced in the wafer cassettes, and further provided for the ability to selectively remove wafers from a plurality of cassettes and place those wafers in a predefined order within the processing chamber. Additionally, it would be desirable if methods and systems allowed for maintaining the wafers in a substantially vertical orientation during all phases of manipulation. Such vertical orientation decreases the likelihood that dust or other contaminants will settle on the surface of the wafers.